The invention provides an improved low pressure mercury vapor discharge lamp, in particular a fluorescent lamp, comprising a glass envelope with an inner wall phosphor coating and with a silicon dioxide (SiO.sub.2) coating between the phosphor coating and the envelope.
It is known to apply to the inner wall of the lamp envelope a continuous, three-dimensional film of a structure of bonded silicon and oxygen atoms (NL-PA 68 13 725). It is a homogeneous coating of a thickness of preferably 0.1 `to 0.4.mu.. The coating is intended to prevent a reaction between the mercury in the lamp and the alkaline components contained in the glass wall which, if the reaction occurred, would result in the production of amalgam and cause a blackening of the envelope, and thus an accelerated reduction of the light out-put and shortening of the lamp life.
It is the subject of the invention to improve the lamp with respect to luminous efficacy, luminous flux and production costs by means of a silicon dioxide intermediate coating.